.header_nav{
	width: 100%;
	height: 35/50rem;
	text-align: center;
	font-size: 24/50rem;
	color: #fff;
	background: #ff2d2d;
	position: fixed;
	top: 0;
	left: 0;
	z-index: 500;
	.header_b{
	 height: 35/50rem;
	 line-height: 35/50rem;
	}
}